Pseudo-random masks for angular alignment

We present an alignment technique that exploits angular correlations by employing a pair of masks, which encode in an angular format pseudo-random sequences. The angular correlator generates peaked irradiance distributions on-axis, provided that the elements of the pair are aligned. Otherwise, the on-axis irradiance distribution decreases to a minimum value. Since the proposed angular correlator is independent of the lateral magnification, it is useful for testing the performance of varifocal lenses. A merit function describes the tolerance to focus errors associated with the location of a small size detector. We use linearly polarized films for showing that the technique also works well with broad band light.